[sebhc] More comments on Heath history - CRT flashover et al

Bob And Bettina Groh rgroh at swbell.net
Tue Mar 28 23:47:46 CST 2006

To add to this story a bit, I had just started working (engineer in the 
Ham Radio department) at Heathkit in the summer of 1977 and purchased 
one of the very first H-89s off the production line. After waiting for 
what seemed like a jillion years (actually about 3 or 4 weeks), they 
started shipping them and I picked mine up at the store at the main 
plant in St. Joseph. But it didn't have a disk drive (i.e. it was 
effectively an H-88 with only a tape interface) because there was some 
sort of a problem involving the disk drives and they were holding them 
until the problem was solved. After several weeks (?? not sure how long 
it took but I did learn to really, really appreciate disk drives after 
coping with a cassette tape drive), the mod kit and the drives were 
finally released. It seemed that, as Lee commented, the disk drives 
(only 40-track, SS SD) were being corrupted by electrical noise from teh 
HV, CRT, et al. The solution was a mu-metal shield.

Didn't know about the 80-track problem but I ran DS DD drives in mine 
with nothing but that mu-metal shield.


Bob Groh
Heathkit Engineer 1977 to 1981

Lee Hart wrote:

>Heath was actually rather brave (or ignorant) to put a computer in the
>same box with a CRT, without any of the usual shielding around the CRT.
>The CRT, flyback transformer, and associated high voltage wiring can
>cause corona, arcing, and electric fields that wreck havoc on sensitive
>The disk drives were the most sensitive to CRT noise. 80-track
>double-sided drives were the worst offenders. Heath finally came out
>with the H88-9 kit to totally enclose the disk drive in a steel box,
>which was carefully bypassed and grounded to keep CRT noise out of it.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sebhcMaillist.heathkit.garlanger.com/sebhc/attachments/20060328/c08b3739/attachment.htm>

More information about the Sebhc mailing list